The load balancing method is described hereinafter by taking an example of 1xEVD0. With 1xEVD0, a terminal is controlled according to a probability transition model. The terminal generates a random number at adequate timing, and the value of the random number is compared with a predetermined threshold, whereupon if a specified condition is met, a transmission rate is updated. The transmission rate is controlled according to a probabilistic process by such an operation as described, thereby preventing occurrence of abrupt variations in the transmission rate. If the abrupt variations occur in the transmission rate, this will disable the terminal from properly controlling transmit power, thereby rendering the terminal uncontrollable. With this in mind, there has been introduced autonomous decentralized control employing probability. The rate is normally controlled in an upward direction. When the rates at respective terminals become higher, transmit power as required increases, so that there occurs an increase in signal reception power on the part of a base station. If there occurs excessive competition to increase the transmit power, terminals on respective boundaries of cells will come to have the transmit power constantly at the maximum level, thereby rendering the terminals unable to obtain desired characteristics, so that it is necessary to suppress the transmit power at an adequate level. For example, according to Evaluation Methodology of 3GPP2, it is stipulated that evaluation on capacity be carried out on a condition that a probability of RoT (Rise over Thermal) exceeding 7 dB is less than 1%. An actual system is operated based on such an upper limit as above. When the signal reception power at the base station reaches such a standard as described, a base station apparatus sets a bit called RAB (Reverse Activity Bit) to “1”. The RAB is worked out based on information such as the signal reception power of the base station, or RSSI (the total signal reception power of the base station apparatus), and so forth. When RoT or an observed value equivalent thereto reaches a specified value, or higher, the base station sets the bit to “1”. Accordingly, the RAB is control information indicating that the signal reception power has reached a specified value. The terminal stops increasing the rate upon detection of the RAB being set to “1”, and conversely, executes control so as to lower the rate with the use of control employing a random number. Since the RAB is transmitted according to instantaneous signal reception power of the base station, control is executed such that a system condition is held in the vicinity of the boundaries where the RAB is set to “1”. The RAB is generated based on instantaneous values of measurement results, however, there has been no stipulation concerning interlace transition to be described later in the present description.
[Non-Patent Document 1]
Standardization Literature: 3GPP2 C. S0024-A v2.0 “CDMA 2000 High Rate Packet Data Air Interface Specification (2005/07) pp. 10-141 to 10-143